The plants of the genus Sceletium are known to contain indole alkaloids such as mesembrenol, mesembranol, mesembrine and mesembranone, the chemical formulae of which are described in U.S. Pat. No. 6,288,104. U.S. Pat. No. 6,288,104 describes mesembrine, mesembrenol and mesembranone as having potent 5-HT uptake inhibitory activity and, thus, as being useful in treating conditions that respond to treatment with a serotonin-uptake inhibitor, such as mild to moderate depression. Mesembrine hydrochloride has previously been reported to be a weak PDE4 inhibitor (Napoletano, M. et al. 2001. Mesembrine is an inhibitor of PDE4 that follows the structure-activity relationship of rolipram. Chemistry Preprint Archive, Volume 2001, Issue 3, Mar. 2001, Pages 303-308).
The applicant has surprisingly found that mesembrenone exhibits potent PDE-4 inhibition properties and, in addition to being useful in treating conditions that respond to treatment with a PDE-4 inhibitor, has dual activity on account of its serotonin-uptake inhibition properties.